The invention relates to a method of cleaning a moving surface, in which cleaning is performed by a doctor blade arranged against the surface to be cleaned, and in which the whole width of the moving surface is cleaned in a direction transverse to its grain direction by means of a doctor blade formed by edges of several blade means.
The invention also relates to an apparatus for cleaning a moving surface, comprising a doctor blade, supporting member arranged to support the blade and means for pressing the doctor blade against the surface to be cleaned, the doctor blade comprising several separate blade means, the edges of which are arranged to form a uniform doctor edge in a direction transverse to the grain direction of the surface to be cleaned, and the doctor edge is at least as wide as the surface to be cleaned in a direction transverse to its grain direction.
Paper, packing, plastic and textile industries use a plurality of different rollers and other cylinder-like members, e.g. drying cylinders and the like for processing products. A problem is, however, that particles from the product to be manufactured, e.g. dye, coating material, dust, fibres, etc, gradually stick on the circumference of rollers and cylinders. Particles stuck on the surface of rollers and cylinders cause problems related to quality, since impurities on the surface of the roller or the like leave marks on products. One solution to the problem is to arrange a doctor against the circumferential surface of the roller or the like, the doctor being a kind of blade which scrapes stuck impurities off.
A problem with prior art doctors is that the doctor blades wear out quickly, whereby the capacity of the doctor for separating dirt decreases considerably, which results in problems related to quality. Furthermore, if the doctor blade is worn, fibres and other impurities get between the blade and the roller, and these may burn and stick on the doctor and roller. Such impurities between the doctor and the roller may cause damage to the circumferential surface of the roller, which in turn may cause undesirable streaks in products. As a consequence, the production line has to be stopped from time to time to change new or repaired doctor blades and rollers. The removed doctor blades are cleaned and sharpened, and the rollers are ground to their shape, and their surface is smoothed for the next change.
A problem associated with the above method is that change of blades and rollers causes a stoppage in production, and furthermore, continuous service of blades and rollers increases costs considerably. An effort has been made to solve the problem by developing more durable materials for doctor blades. Experiments have been carried out by using ceramic blades, blades made of polymer and blades made of a plurality of different alloys, but the improvements have, however, been insufficient. A further solution has been to oscillate doctor blades in the direction of the roller so as to improve durability of blades and rollers. Such an apparatus has been disclosed in Finnish Patent 22388. Oscillating movement cannot, however, remove impurities stuck between the blade and the roller adequately, which causes a fault on the circumferential surface of the roller, which results in a quality defect in the product. A disadvantage common to all prior art doctors is that in order to service and maintain them in working order, a production line has to be stopped for service or for changing substitute devices. Furthermore, it has not been possible to improve the durability of doctor blades sufficiently either by developing blade materials or the oscillating movement. Finnish Patent 54076 discloses an endless, ribbon-type doctor blade. A disadvantage of this solution is that if the ribbon-type blade is damaged, e.g. a cut is formed in it, the whole blade ribbon has to be changed. Furthermore, in the ribbon-type arrangement the blade material has to be flexible, and thus e.g. ceramic blades cannot be used.
An object of this invention is to provide a new method for cleaning different moving surfaces, which allows more undisturbed production and higher production rate than the prior art solutions.
A further object of the invention is to provide a new doctor apparatus eliminating the drawbacks of the prior art.
The method of the invention is characterized in that the blade means are connected to form a closed loop, and that the blade means are moved during cleaning in a direction transverse to the grain direction of the surface to be cleaned.
The apparatus of the invention is characterized in that blade means are connected to form a closed loop and that the blade means are connected in such a manner that they can be moved in relation to the surface to be cleaned.
The basic idea of the invention is that the doctor blade comprises several smaller separate blade means, which are arranged one after another, and the edges of which form a uniform doctor edge in a direction transverse to the grain direction of the moving surface, the doctor edge being at least of the same width as the moving surface. Another idea of the invention is that the doctor blade can be moved to a special service point, where it can be serviced and repaired during the run. A further idea of an embodiment of the invention is that the blade means are connected to form a closed loop, which is arranged to move around return wheels. The basic idea of a further embodiment is that the blade means are arranged to move continuously, and the speed of the motion in a direction transverse to the surface to be cleaned can be adjusted, if necessary. At the return wheels, the blade means can be easily cleaned and the blades sharpened with an automatic sharpening unit, since the blade means are apart from one other.
An advantage of the invention is that it is not necessary to stop a production line for service and repair of the doctor, but blade means can be serviced during the run. This allows to save on costs considerably. Furthermore, moving surfaces, such as rollers, wires, belts, etc. will last longer, since they are always cleaned by a doctor which is in good condition. A further important advantage is that the quality of products improves, since there will be no variation in quality due to wearing of doctor blades and impurities. The apparatus of the invention also allows increase in the processing speed and production without interruptions.